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README.md

llvm-j

llvm-j is a Java library for parsing and modifying LLVM IR.

The goals of llvm-j are:

  1. Provide an easy to use LLVM IR parser that feels like a native Java library (compared to a collection of JNI bindings).
  2. Make it easy to upgrade to higher versions of LLVM without API changes. This is important since LLVM updates may change the LLVM core API - we want our users to be able to use llvm-j independent of such changes, and allow them to use new LLVM versions without a need to update their code.

To achieve these goals, llvm-j uses Java bindings for the original LLVM C parsing library with java native access (JNA), but provides proxy classes for the most common parsing tasks. This way, the user never has to call the C bindings directly, but can work with our own, Java-like API (e.g., we aim to throw Exceptions for illegal states instead of returning values with a special error meaning).

The Java bindings for the LLVM C parsing library are automatically generated with JNAerator. Through this, it is easy to update the bindings to new versions of LLVM, and the user doesn't have to change any code since the llvm-j API stays the same.

Currently, we use LLVM 3.9.1.

Use

The proxy classes are provided in Java package org.sosy_lab.llvm_j for easy use. The original bindings are located in org.sosy_lab.llvm_j.binding.

If you didn't put the LLVM 3.9.1 shared library in one of your system directories for library lookup, you can tell llvm-j in which directory the library is in in two ways:

1. Provide system property `jna.library.path` to Java, for example
   `java -Djna.library.path=additional/lookup/path -jar appParsingLlvm.jar`
   or
2. Add the directory in the code
   with static method [`Module#addLibraryLookupPaths(List<Path>)`](ADDLINK),
   *before* calling `Module#parseIR(String)`.

To parse LLVM IR, call static method Module#parseIR(String) with the file to parse as argument. Currently, llvm-j only understands LLVM IR in bitcode format (usually file suffix *.bc). Method Module#parseIR(String) will return a Module object

Development

To build this project yourself, you should first clone or download this repo.
The project consists of three components:

  1. The automatically generated Java bindings of the LLVM library
  2. The Java API
  3. The shared library of LLVM

We use ant to manage our build process. If it is not yet installed on your system, you will have to do so.

Generating Bindings

Generated bindings are already provided and part of the project. Thus, generating them manually is usually not necessary.

If you still want to re-generate the bindings, you require an installation of LLVM that includes the LLVM C headers. If /path/to/llvm includes the LLVM C-headers directory /path/to/llvm/includes/llvm-c, run:

    ant bindings -Dllvm.home=/path/to/llvm

Notice that new bindings may require modifications to the proxy classes, since the LLVM C API may change over time.

Build Java API

To compile the Java API, run ant in the project's root directory.
To create a jar file for distribution, run ant jar.
The output of the command will tell you the name of the created jar file.

The jar file does not include the shared libraries of LLVM.

Get Shared Library of LLVM

llvm-j dynamically loads the shared libraries of LLVM, so they must be available for your machine in the right version. For convenience, we provide a mechanism to automatically download and extract the shared libraries from an Ubuntu package (for 64 bit systems). These libraries should work on most Linux distributions.

Library Download

Requirements: We assume that you have common command-line tools installed.
In addition, tool chrpath is required. On Ubuntu, it can be installed by running sudo apt install chrpath.

Download: To automatically download the library and its dependencies, execute on the command-line, from the project's root directory:

    ant download-library

The libraries will be automatically downloaded and put into directory lib/native. You can then either move them to a system path for libraries (e.g., /usr/local/lib) or put them in your project.

Others ways to get the library

If you use Windows, macOS, or the provided libraries do not work on your system, you can

  1. use an LLVM package that includes the shared libraries for your system or
  2. compile the shared libraries yourself.

For both options, make sure that you use the correct version of LLVM.

Creating JavaDoc

To create the JavaDoc, run ant javadoc in the project's root directory.

Tools for Code Quality

We provide some checks that may help you in writing good and correct code. You can run:

You can run ant all-checks to run CheckStyle, the Eclipse compiler, the JavaDoc task (which performs linting for JavaDoc) and SpotBugs.

These tools are, of course, not enough to ensure good code quality, but only some helpers.

Currently, the proxy classes aim at parsing LLVM IR bitcode, not modifying it. If you miss any functionality, please create a new issue or message us to help us improve llvm-j!

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